1. Field of the Invention
The invention relates to a transmission with a countershaft and a planetary reduction gear unit for an automobile.
2. Description of the Prior Art
German Offenlegungsschrift 34 15 479 ('479) describes a manual transmission with a countershaft and a planetary reduction gear unit. The transmission in the '479 patent has fixed and loose pinions and gears which form pinion and gear pairs that are in constant mesh with one another and which are supported by, and driveably connectable to, an input shaft and countershaft or output shaft by synchronisers mounted on the shafts to select the individual gears. The planetary reduction gear unit of the '479 patent comprises a ring gear fixed in the transmission housing, a sun wheel driven by way of a pinion and gear pair and mounted on a sleeve shaft concentrically embracing the output shaft, and a planet pinion carrier connected to the output shaft.
In the manual transmission of the '479 patent there is provided, in addition to the sleeve shaft carrying the sun wheel, a further sleeve shaft carrying further a fixed pinion and gear and a loose gear adjacent a synchroniser. This additional sleeve shaft is connectable to the sleeve shaft of the sun wheel. Furthermore this further sleeve shaft is connectable to the output shaft through a fixed pinion carried on the sleeve shaft and through a synchroniser carried on the output shaft.
In the '479 manual transmission it is stated that because the subsequent planetary reduction gear unit enables the reduction ratios of the individual pairs of pinions and gears to be made smaller, the overall design of the transmission can be more compact.